Method and apparatus for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold

ABSTRACT

Apparatus for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold. The apparatus includes a source of granular mold flux, and a transport apparatus interconnected with the source of granular mold flux and capable of moving the granular mold flux at varying rates onto the top of a strand of steel being cast within a continuous casting mold. A sensing apparatus is provided which is capable of determining a parameter of the mold flux on the top of the strand of steel being cast, which sensing apparatus may be a temperature sensor or a level sensor. A control is also provided which is responsive to the sensing apparatus to regulate the rate of flow of the granular mold flux onto the top strand of steel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This aplication claims priority from U.S. provisional application Ser. No. 60/279,831 filed Mar. 29, 2001.

TECHNICAL FIELD

[0002] The present invention relates generally to the metal casting field wherein molten steel may be continuously cast into a slab of steel, and more particularly to method and apparatus for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold.

BACKGROUND OF THE INVENTION

[0003] It is customary to apply a mold flux, which may be a powder or granular material, onto the top of a slab during continuous casting of a molten metal, typically steel, the flux turning into slag when sufficiently heated by the molten steel. In the past, it has been common to maintain about 1-2 inches of flux or slag on top of the mold during casting. It is common today to merely sweep the mold flux onto the top of the slab when desired, the flux being provided in 10 kg. bags. This system works, but it is manpower intensive, and it requires constant monitoring by a skilled operator to maintain 1-2 inches of flux or slag on top of the mold during casting. In addition, it is environmentally unfriendly as there is a lot of refuse from the empty 10 kg. bags.

[0004] U.S. Pat. No. 4,084,626 illustrates a device for feeding a mold flux in the form of a powder. The powder has poor flow characteristics, and thus a screw feed mechanism is used, which screw extends between an intermediate hopper (or bin) and the top of the slab being cast. This form of device is somewhat expensive and, in fact, is not typically used in industry because of its cost and unreliable operation. One of the problems with this device is that the layer of flux may become too thin, i.e., less than one inch in thickness, or it may become too thick, i.e., more than 3 inches in thickness. Thus this device requires constant supervision.

[0005] U.S. Pat. Nos. 4,595,045 and 5,158,129 disclose method and apparatus for applying a layer of flux to the top of a slab being cast. In both of these designs, the delivery pipe (or supply pipe) is positioned slightly above the predetermined powder height, so that flow through the pipe is regulated by how fast the flux material flows away from the discharge end of the pipe. Thus, when the powder level drops below the delivery end opening, material flows from the pipe. This form of apparatus, which relies solely upon the flow of material away from the delivery pipe, has not always been satisfactory since occasionally the end of the delivery pipe will become blocked by slag or the like.

[0006] U.S. patent application Ser. No. 09/498,220 discloses a method and apparatus for introducing a granular mold flux onto the top of a slab being cast within a continuous casting mold wherein the flux may be introduced at a substantially constant rate. In one form, a variation of which is illustrated in FIGS. 3 and 4 of this application, the apparatus consist of a vacuum transfer system which transfers the granular mold flux from a source of granular mold flux, which may be a large bulk bag (approximately 4-5 ft. on each side) to an intermediate hopper provided with a sensor a suitable distance above the bottom of the intermediate hopper. The flux is then delivered through at least one delivery tube assembly onto the top of the slab being cast. In the embodiment shown in FIGS. 2 and 2A of this application, the flow of flux through the delivery tube assembly is assured by an inline air pump which maintains flow at varying rates through the delivery tube assembly. If it is not right, as will be determined via a visual inspection of the top of the slab, it will be adjusted. As can be seen this form of apparatus also required frequent manual adjustments to insure that the delivery rate is equal to the rate of the flux which is being consumed.

OBJECTS AND SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide an apparatus for automatically controlling the feed rate of the flux being delivered, so that the delivery rate is equal to that rate of the flux which is being consumed during casting. More specifically, it is an object of the present invention to provide an apparatus which includes a sensing apparatus which is capable of determining a parameter of the mold flux on the top of the strand of steel being cast, which sensing apparatus may be either a temperature sensor or a level sensor. A control is also provided which is responsive to the sensing apparatus, and which automatically regulates the rate of flow of the granular mold flux onto the top of the strand of steel.

[0008] The foregoing will become more apparent after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of this invention is illustrated.

BRIEF DESCRIPTION of the DRAWINGS

[0009]FIG. 1 is a schematic side view of a continuous casting mold which receives molten steel from a tundish via a ceramic pouring tube.

[0010]FIG. 2 is a partial perspective view of a prior art transport apparatus for introducing a granular mold flux onto the top of a slab being cast within a continuous casting mold, wherein an operator can control the flow rate so that ideally the flux will be introduced into the mold at a substantially constant rate.

[0011]FIG. 2A is a detail of the prior art transport device shown in FIG. 2.

[0012]FIG. 3 shows an alternative transport apparatus for introducing a granular mold flux onto the top of a slab being cast within a continuous casting mold, this view also illustrating a sensing apparatus of this invention which is capable of determining the temperature of the mold flux on the top of the strand of steel being cast, and also illustrating a control responsive to the temperature sensing apparatus to regulate the rate of flow of the granular mold flux onto the top of the strand of steel.

[0013]FIG. 4 is a view similar to the view shown in FIG. 3, but showing a device for measuring the level of the flux upon the strand of steel being cast, the device being a laser distance measurement device.

DETAILED DESCRIPTION

[0014] In the following description of the various embodiments of this invention, common parts will be represented by the same reference numerals. With reference initially to FIG. 1, the continuous casting mold, which in the preferred embodiment is a water-cooled copper mold, is indicated by reference numeral 12. The slab being cast is indicated by reference numeral 14. The slab material, which in the preferred embodiment is molten steel, is initially fed from a tundish 16 through a ceramic pouring tube 18. The granular mold flux, which is fed onto the top of the slab in accordance with this invention, is indicated by the reference numeral 20. The flux 20 will not only be disposed on the top of the slab 14, but will also extend between the slab 14 and the mold 12 as indicated in the drawings. In this regard, the flux 20 becomes a liquid slag when heated sufficiently by the liquid steel. This molten slag is what fills the gap between the steel shell and mold wall.

[0015] A prior art design is illustrated in FIGS. 2 and 2A. In this embodiment a stationary primary hopper 88 is provided, which hopper may be filled with a granular mold flux in any manner, i.e., from individual bags or from a bulk source. The hopper has a discharge pipe or tube 90 to which is connected an upper and lower “T” fittings 92, 96 and an intermediate nipple 94. The “T”s and nipple serve as an intermediate hopper, and the lower “T” 96 is provided with a plug 98. A pair of inline air pumps 76 are connected directly to the intermediate hopper, and flux will be delivered by the pumps 76 to the mold through delivery tube assemblies 72. The air pressure to each of the inline air pumps is regulated by an I/P device 84 which receives shop air 80. The output of the I/P devices is controlled by a control panel 70 (FIG. 2A) which is connected to each of the I/P devices by electrical control lines 82. It has been found that in some situations the selected I/P devices are incapable of supplying sufficient air volume to deliver the desired quantities of flux, either because of the distance between the inline pumps 76 and the mold 12, or because the mold requires large quantities of flux. In these situations an air volume booster 100 of conventional design may be provided to increase the flow of air, but to maintain it at the desired pressure.

[0016] In the process of continuous casting, mold flux is applied to the strand surface and consumed at a rate dictated by casting conditions. Currently, the flux feeder shown in FIGS. 2 and 2A is operated manually. An operator changes the set point on the feeder control box 70 to meet the mold flux consumption requirements at the caster. The electrical signal through lines 82 gives a proportional pressure output that controls the air flow and flux feed rate.

[0017] It is important to maintain a constant layer of mold flux covering the steel. Manually controlled, the feeder must be adjusted as casting conditions change (primarily speed) and requires operator input. To eliminate the need for manual adjustments, two automatic control systems are discussed.

[0018] Surface Temperature Measurement Control

[0019] In FIG. 3 a sensing apparatus is disclosed which includes a device for measuring the surface temperature of the mold flux upon the strand, which sensing apparatus is coupled to a control responsive to the sensing apparatus to regulate the rate of flow of the granular mold flux onto the top of the strand of steel. Initially, it should be noted that mold flux is a very good insulator covering the steel. Thus, the liquid steel surface is at 1500 degrees Celsius in the mold, and the mold flux surface temperature is in the approximate range of 200-400 Celsius, dependent on thickness of the unmelted layer. An ideal mold flux covering is 1-2 inches in thickness on the steel. The surface temperature of the flux varies as the flux depth changes.

[0020] Because the steel temperature is constant, there exists a constant temperature gradient within the flux layer. The apparatus shown in FIG. 3 provides a steady fluidized feed rate to the mold. To this end, an infrared temperature device measures the surface temperature and outputs a 4-20 mA signal to a temperature controller that automatically maintains a constant temperature by varying the feed rate.

[0021] In the prior art the operator would change the temperature set point to control the mold flux layer thickness. In the design shown in FIG. 3 the sensor will output a mA signal proportional to the temperature, and the controller will vary the output to the feed box increasing or decreasing the feed rate to keep the temperature the sane as the set point.

[0022] Distance Measurement Control

[0023] As shown in FIG. 4, a laser device can also be used to control the feed rate by keeping a constant flux layer on the steel surface. With a constant steel surface level, the laser can control the feed rate by maintaining a set point based on laser distance from the surface. The output from the laser is a 4-20 mA signal proportional to the distance.

[0024] The temperature controllers are used and output a signal to the feed box based on the set point and process variables. The controllers will maintain the laser distance reading from the flux surface, therefore keeping a constant powder layer with constant steel level. If a larger flux layer is desired, the set point is increased.

[0025] Both control processes can only be used combined with the flux feeder shown in FIGS. 2 or 2A, or with the feeder shown in FIGS. 3 and 4 which further includes a bulk source of granular mold flux and a vacuum transfer device which feeds a hopper similar to the hopper 88 of FIG. 2. The feeders maintain a steady, fluidized feed rate of mold flux. With this type of feeding, it is easy to determine surface temperature and surface distance and maintain tight control of these parameters.

[0026] While preferred forms of this invention have been described above and shown in the accompanying drawings, it should be understood that applicant does not intend to be limited to the particular details described above and illustrated in the accompanying drawings, but intends to be limited only to the scope of the invention as defined by the following claims. 

What is claimed is:
 1. Apparatus for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold comprising: a source of granular mold flux; transport apparatus interconnected with the source of granular mold flux and capable of moving the granular mold flux at varying rates onto the top of a strand of steel being cast within a continuous casting mold; sensing apparatus capable of determining a parameter of the mold flux on the top of the strand of steel being cast; and control responsive to the sensing apparatus to regulate the rate of flow of the granular mold flux onto the top of the strand of steel.
 2. The apparatus as set forth in claim 1 for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold wherein the sensing apparatus includes a device for measuring the surface temperature of the mold flux upon the strand.
 3. The apparatus as set forth in claim 2 for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold wherein the device for measuring the surface temperature is an infrared temperature sensor.
 4. The apparatus as set forth in claim 1 for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold wherein the sensing apparatus includes a device for measuring the level of the flux upon the strand of steel being cast.
 5. The apparatus as set forth in claim 42 for controlling the flow of granular mold flux onto the top of a strand of steel being cast within a continuous casting mold wherein the device for measuring the level of the flux is a laser distance measurement device. 